<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>Document</title>
    </head>
    <body>
        <script>
            let arr = [1, 2, 3, 4, 5, 1, 2];
            function unique(arr) {
                return arr.filter(function (item, index) {
                    return arr.indexOf(item) === index;
                });
            }
            console.log(unique(arr));
        </script>
    </body>
</html>
